1. Field of the Invention
The present invention generally relates to a multifunction power conversion device, and more specifically to a multifunction power conversion device for generating a current sensing zero detection signal by combining a sensing signal from a primary coil and an auxiliary sensing signal from an auxiliary coil to transmit to a single signal pin such that a digital control unit determines if a current flowing through a secondary coil reduces to zero according to the current sensing zero detection signal, and further detects valley and a number of valley for the current of the secondary coil, thereby turning on a switching transistor to reduce switching loss, and performing a process of current sensing to determine whether to turn off the switching transistor when the switching transistor is turned on.
2. The Prior Arts
For various electronic devices, some specific electric powers are required for normal operation. Some integrated circuits (ICs), for instance, need 5V or 3V, electric motors need 12V DC power, and the backlight modules for LCD monitor need a much higher voltage like 1150V. To meet the requirement for power source, high quality and efficient power converters have become a key component and been progressively developed and widely used. Currently, the power converter is one of the key components in electronic products.
As shown in FIG. 1, one of the power conversion circuits in the prior arts generally comprises an input filter unit 10, a transformer TR, a switching transistor 20, a driving controller 30, a feedback unit 40 and an output unit 50. The transformer TR substantially comprises a primary coil LP, a secondary coil LS and an auxiliary coil LA. The switching transistor 20 is a traditional MOS (metal oxide semiconductor) power transistor. The input filter unit 10 receives and filters an AC power VAC to generate and transmit an input power VIN to the primary coil LP. The drain of the switching transistor 20 is connected to the primary coil LP, and the source of the switching transistor 20 is connected to the sensing resistor RS to generate a current sensing signal CS. The gate of the switching transistor 20 is connected to the driving controller 30 to receive the driving signal GATE from the driving controller 30.
The secondary coil LS generates a sensing current through induction of the primary coil LP, and the output unit 50 generates an output power VOUT based on the sensing current. The feedback unit 40 receives the output power VOUT to generate and transmits a feedback comparison signal COMP to the driving controller 30. The auxiliary coil LA generates an auxiliary sensing voltage by induction of the primary and secondary coils LP/LS. Further, the auxiliary sensing voltage is divided by a first dividing resistor R1 and a second dividing resistor R2 connected in series to generate a zero detection signal ZC at the connection of the first dividing resistor R1 and the second dividing resistor R2, which is further transmitted to the driving controller 30.
The driving controller 30 employs the zero detection signal ZC to perform a zero detection process to find the valley of the current flowing the secondary coil LS, and determine the conduction state. At the same time, the feedback comparison signal COMP is used to obtain the value of the output power VOUT such that the driving controller 30 generates the driving signal GATE for turning on/off the switching transistor 20. In other words, when the switching transistor 20 is turned on, the turn-on voltage increases to cause the current sensing signal CS to increase. When the current sensing signal CS is larger than the preset value, the switching transistor 20 is turned off. Additionally, when the switching transistor 20 is turned off, the auxiliary sensing current flowing through the first dividing resistor R1 and the second dividing resistor R2 first increases up to a peak value, then reduces and causes oscillation. Thus, the driving controller 30 utilizes the zero detection signal ZC to detect the zero, that is the valley, so as to determine whether to turn on the switching transistor 20 for minimal switching loss.
However, one of the shortcomings of the above power conversion in the prior arts is that the driving controller has to configure two signal pins to receive the sensing signal from the primary coil and the auxiliary sensing signal from the auxiliary coil, respectively. The area of the first and second dividing resistors is quite large. As a result, the cost of the circuit layout increases, particularly for the integrated circuit.
Therefore, it is greatly needed for a new multifunction power conversion device for dynamical detection, wherein the current sensing zero detection signal is generated by directly combining the sensing signals from the first and auxiliary coils and transmitted to the single sensing pin. The digital control unit utilizes the current sensing zero detection signal to determine if the second side current discharges to zero, and detects the valley and the accumulated number of the valley so as to determine whether to turn on the switching transistor. When the switching transistor is turned on, the current limiting process is performed to determine whether to turn off the switching transistor. It is obvious that switching loss is greatly reduced, efficiency of power conversion is improved, and industrial utility is provided. In particular, the digital control unit operates in a fully digital manner to meet actual requirements by just updating the firmware program to greatly enhance flexibility in application, thereby overcoming the above problems in the prior arts.